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Gregor Mendel
Genetics Experiments
With Pea Plants
Mendel Noticed
Pea Plants varied by:
height, color of flowers, position of
flowers, seed color, seed shape,
pod color, pod shape
Mendel Hypothesized
Mendel Hypothesized
Variations in pea plant appearance was due to something (some information) passed along during reproduction by the parent plants.
Mendel’s Experimental Design
Mendel’s Experimental Design
Mendel raised pea plants to “breed true,” I.e. tall only produced tall, short only produced short
Mendel’s Experimental Design
Mendel raised pea plants to “breed true,” I.e. tall only produced tall, short only produced short
Mendel crossed one true-breeding variety with the alternate true-breeding variety, e.g. tall x short
P1 Tall X Short
P1 Tall X Short
F1 All Tall
P1 Tall X Short
F1 All Tall
F2 3/4 Tall 1/4 Short
Mendel Hypothesized
That something was passed from parents to offspring to determine height; he called this an allele
P1 Tall X Short
T t
F1 All Tall
T
F2 3/4 Tall 1/4 Short
T t
Mendel Hypothesized
That something was passed from parents to offspring to determine height; he called this an allele
Further, since the t allele was “hidden” in the F1, but reappeared in the F2, plants must have a pair of alleles for each trait.
P1 Tall X Short
TT tt
F1 All Tall
Tt
F2 3/4 Tall 1/4 Short
T? tt
When an organism had a pair of alleles the same, e.g. TT or tt, he called this homozygous
When an organism had an unlike pair of alleles, e.g. Tt, he called this heterozygous
These terms refer to an organism’s genotype
The appearance of the organism he called it’s phenotype
Practice VocabEx. Plant Height
Genotype
Phenotype
Pure or Hybrid
Homozygous/
Heterozygous
More practice
Genotype
Phenotype
Pure or Hybrid
Homozygous/
Heterozygous
Ex. Flower color
Mendel proposed several principles regarding his
findings If an organism is heterozygous and
only one phenotype appears, this is the dominant phenotype, the alternate is the recessive phenotype
When an organism reproduces, allele pairs must segregate and only one member of each allele pair is passed along to the next generation.
Solving Genetic Problems
T T t t
T T t t
T X t = T t F1
Punnett Square
TT X tt
T
T
t t
Tt Tt
Tt Tt
Genotype
4/4- Tt
Phenotype
4/4- Tall
Practice Space
Test Cross
What is the genotype of a short pea plant?______
What is the genotype of a tall pea plant?_____ or _____
Mendel developed a way of testing whether the tall plant is homozygous or heterozygous. It was the test cross
Test Cross problem
T_ X tt
Independent Assortment
The inheritance of any characteristic is independent of the inheritance of any other characteristic.
Ex. The inheritance of height is independent from pea color.
Mendel provided evidence for this through dihybrid crosses.
Dihybrid Cross
TtPp X TtPp
To solve this problem you can use a 16 block punnett square or the Forkline method.
16 Block Punnett Square
Fork Line Method
Ex. TtPp X TtPp
Practice with Fork Line Method
Practicing Punnett Squares
Inheritance patterns that Mendel did not know
about Incomplete dominance Codominance Multiple alleles Polygenic Inheritence Sex Linkage
Incomplete Dominance
Incomplete dominance does not involve an allele that masks recessive allele. Instead there is a blending of the two alleles.
Ex. Red flower X White flower =Pink
Cross Two Pink flowering plants
Example
Cross a two pink flowering plants
RW X RW
Codominance
Codominance does not involve an allele that masks recessive allele. Instead both alleles show in the phenotype
Ex. Brown horse X White horse =Spotted
Cross a brown horse with a spotted horse
Codominance Exmple
Cross a brown horse with a spotted horse.
BB X BW
Multiple Alleles
Some phenotypes can be determined by more than two alleles.
Ex. ABO Blood typeGenotypes Phenotypes
AA - A Blood Type
AO - A Blood Type
BB - B Blood Type
BO - B Blood Type
OO - O Blood Type
AB - AB Blood Type
Blood Type Problems
Cross a heterozygous A blood type with a heterozygous B blood type
iAiO X iBiO
Polygenic Inheritance
The inheritance of some characteristics are determined by more than two alleles.
Ex. Skin color, eye color, height, and noses. Phenotypes of polygenic inheritance are a result of the blending of many genes.
Sex Linkage
Who determines the sex of the baby?
How would a gene found on the X chromosome be inherited and expressed differently in males vs. females?
Sex Inheritance
X Y
X
X
XX XY
XX XY
Sex Linked ProblemsX-Linked
Color Blindness is carried on the X Chromosomes. It is recessive.
What are all of the different possible combinations of genotypes an individual could have?
Sex Linkage Problem
Cross a Colorblind male with a woman who is a carrier for colorblindness.
XcXC X XcY
Are you color blind?Lets find out together
http://colorvisiontesting.com/online%20test.htm
Practice Sex Linkage Problems
